My opinion summed up is that it is unethical and the animal industry as it exists today should be abolished and we should move to a plant based future for food, clothing and other items as it is the only sustainable and ethical path.
In this essay however I will only use veganism as an example of the possible effects and reasoning for and against consumer activism. Keep in mind most of what I say will also apply to other types of individual changes people push for.

There is the point that “consumer activism” meaning to try to live more ethically by consuming different kinds of products from different companies or boycotting things all together, is liberal nonsense because it is ludicrous to claim that the average person holds any responsibility over the state of the earth, considering how this is very much the cause of the ultra-rich and big companies, and you buying palm oil or not will essentially have 0 impact on the state of the world. As it barely has any material effect on anything.

This is the point laid out in the song “cognitive dissonance blues” by the narcissist cookbook.

And I want to make clear that I understand this message and also agree with it in many ways as well as understand the frustration of it.
I agree that individual changes alone won't fix anything and you for example don't get rid of the animal industry by having enough people go vegan
However I do believe there is still value to individual change on some level, however before that I want to talk about some more “counter arguments” in this discussion.

Critiques:

"No ethical consumption under capitalism"

This is missing the point.
On one hand just because there is exploitation everywhere doesn't mean there are different extends of harm made.

"It just makes people think they are doing good and turns them away from “actual” solutions"

Valid. This can be very much a liberal thing
I personally can't stand the thought of eating dead animals at this point, it doesn't make me feel superior or that I'm specifically helping but it does make me feel better to not feel that maybe irrational guilt.
So there is certainly an aspect of people feeling better from it. However I think there is still some actual point to it regardless that I'll explain in a second.

"It's Classist"

It's true that many things associated with consumer activism are connected to classism, however the response “some people can't afford it, therefore I don't need to try” is dumb if you personally do have the classist privileges to do something.
You could even argue that you, as someone who has money should, buy ethically because then for the higher demand the prices will go down, making ethical consumption more affordable (which I will go more into later on).
Also some things aren't connected to classism
Things like DIY clothing, second hand, going on bicycles (if the infrastructure and your body allow it) are things that are also the cheapest alternatives because many sustainable options are also cheap in nature

So why do I think its good then if I also believe we ultimately need systematic change and these individual things wont fix anything by themselves?

It Spreads awareness

More people hear about as it is not something that only comes up in some random political discussions but rather something that can be seen throughout the day to day actions of people which makes it more visible.
More people will therefore be aware of these issues.

It Prevents hypocrisy

What do you think how serious people would take for example vegan activists if vegans would still pour money in the same industry they find abhorrent and immoral.
We already see people trying to call put hypocracy on activists all the time, even Greta Thunberg who travels the world with a sail boat will be “called out” for using things like phones. Now that is stupid of course and ridiculous but if people wouldn't put any effort whatsoever to change their personal behaviour I do think the general reaction to activists would be: “you cant even change your personal life and yet expect all of us to live different” to much greater extend than it is happening now
which leads to the next point

Lead by example

People doing this individual change shows that is possible and viable.
Many used to believe you can't live on a vegan diet healthily, now that has changed.
It is showing how a life in the future could look like in small bits by having many lived examples.

Changes the market

While it doesn't change the market in the sense that the companies go away once you try to avoid them.
And even here the argument that if just enough people boycott something it would go away doesn't apply necessarily, as all the people going vegan hasn't exactly changed how many animal products are being produced for example.
Yes the companies are losing money but its balanced out through all the government subsidies they receive.
So tax money that they get, which the animal industry receives significantly more of than any other food sector because of lobbying (aka corruption).
So they produce the same amount, it just goes to waste since they don't sell as much anymore (which is the sort of stuff that happens in a society that produces not for needs but for profit)
One thing that does happen however is we see many more vegan alternatives.
Which plays again into how this just becomes a more viable way to live.
If you would have tried to convince someone to go vegan 40 years ago they would't have considered for second since back then vegan meant just vegetables, fruits, nuts and other basic plants (which can of course be a completely fulfilling diet and there is more than enough variety in plants to make this enjoyable), however now with there being an alternative for every kind of food, people won't feel like they are “giving up” anything
(and yes you could argue that this convenience of “giving up” nuggets for example is a pretty bad justification but that's not the point
Convenience like this matters to many and whether or not its justified people will act based on it so it needs to be considered)
and of course these products are also becoming more affordable through this which also plays into it being more viable.
And all of this also again spreads more awareness as people will see these things everywhere now.
(This does however lead to green washing which can lead to people doubting all of it more again, because they simply see all of it as nothing more than companies trying to act nice)

The position may be summed up by saying we ultimately need systematic change, however individual change if not necessary, will at least be very helpful in getting people to push for said systematic change.
Again think of asking someone what they think about outlawing the animal industry decades ago vs how many people now are at least for abolishing factory farming (which btw is over 90% of the industry).
People are becoming more aware of the issues and since they see alternative ways of living as more viable, they are, at least in theory, more on the side of systematic change.
This isn't the same as class consciousness but it can still be helpful overall in getting people to care

And lastly id also like to touch on the whole boycott of the harry potter legacy game.
The main argument here, which is somewhat different from what I have laid out in this essay, is that of symbolism.
Imagine you are on the street and a person approaches your trans friend and insults them heavily and talks about how they should die and are some sort of abomination.
And then that person hands you a CD of some music they made and you hand them a dollar.
Of course giving that dollar or not is not going to have a significant impact on that persons wallet, but think about the kind of message you you are sending to the trans people around you.
Think about how this just signals how quickly you are willing to give up your allyship for some mediocre entertainment.
That's not to say you are a transphobe or that you can't still overall be a huge ally but the message you are sending out is that you are willing to tolerate hateful people in society as long as they make art you like.

for a deeper dive into this specifically I highly recommend these 2 videos:
Hogwarts Legacy, JK Rowling, and Trans Advocacy
I'm Done With JK Rowling